{	30 January 2011. Individual Olympiad. Problem set: http://neerc.ifmo.ru/school/io/archive/20110130/problems-individual-20110130.pdf
	Problem A
	Points: 100	
}

uses SysUtils;
var m,a,k:int64; n,i:integer;
begin
reset(input,'airplane.in');
rewrite(output,'airplane.out');
readln(m,n,a);
for i:=1 to n do begin
  read(k);
  inc(m,k);
end;
if a<>1000 then writeln((m*a)/(1000-a):0:6) else writeln('Impossible');
end.
 